NOVEL COUPLED FOLDED WAVEGUIDE RESONATOR FILTER

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1 frequency of 5.41 GHz with a measured peak output of 3.50 dbm at a bias condition of V ds 1.5 V, I ds 10 ma, and V gs 0.2 V. The second and third harmonic suppressions were measured as db and db, respectively, and the phase noise is measured as dbc/hz, at an offset of 1 MHz. In Figure 5, for comparison, we show the measured fundamental output spectrum and harmonic performance of the reference CPW oscillator with the CCPW in Figure 3 replaced by a conventional CPW line without any corrugation. The output power of the reference oscillator oscillating at 5.58 GHz was measured as dbm, with only a db rejection of the second harmonic and a phase noise of 107 dbc/hz at 1 MHz offset at the same bias conditions of V ds 1.5 V, I ds 10 ma, and V gs 0.2 V. These results constitute a db reduction in second harmonic suppression and results in DC to AC power efficiency improvement of 7.2% of the newly developed CCPW-based oscillator when compared to those of a conventional CPW oscillator without the CCPW structure. The phase noise improvement due to the higher phase slope of the CCPW-based oscillator is measured as 8 db at 1 MHz offset from the carrier frequency. 5. CONCLUSION In this article, a novel oscillator that incorporates a uniplanar CCPW EBG structure as a resonator component of the conventional CPW oscillator circuit was presented. The introduction of the CCPW EBG structure was verified to be effective in reducing the phase noise, and in enhancing the harmonic performance and DC-AC power efficiency of the oscillator circuit in a very small chip size increment. The small size and uniplanar structure characteristic of the circuit can be easily applied to MMIC applications of the circuit while avoiding the drawbacks of the conventional DGS-based EBG oscillators. ACKNOWLEDGMENT This research was supported by EMERC at CNU and ADD, through the RDRC at KAIST. REFERENCES 1. C.Y. Hang, V. Radisic, Y. Qian, and T.Itoh, High efficiency power amplifier with novel PBG ground plane for harmonic tuning, IEEE MTT-S Int Microwave Symp Dig 2 (1999), A. Griol, D. Mira, A. Martinez, J. Marti, and J.L. Corral, Microstrip multistage coupled ring band-pass filters using photonic bandgap structures for harmonic suppression, Electron Lett 39 (2003), Y.J. Sung and Y.S. Kim, An improved design of microstrip patch antennas using photonic bandgap structure, IEEE Trans Antenn Propag 53 (2005), H.W. Liu, X.W. Sun, and Z.F. Li, A VCO with harmonic suppressed and output power improved using defected ground structure, Proceeding of SBMO/IEEE MTT-S IMOC 2003 (2003), Y.T. Lee, J.S. Lim, J.S. Park, D. Ahn, and S.W. Nam, A novel phase noise reduction technique in oscillators using defected ground structure, IEEE Microw Wireless Compon Lett 12 (2002), Z. Du, K. Gong, J.S. Fu, B. Gao, and Z. Feng, Influence of a metallic enclosure on the S-parameters of microstrip photonic bandgap structures, IEEE Trans Electromagn Compatibility 44 (2002), J.Z. Gu, W.Y. Yin, R. Qian, C. Wang, and X.W. Sun, A wideband EBG structure with 1D compact microstrip resonant cell, Microw Opt Tech Lett 45 (2005), 386, S.J. Kim and N.H. Myung, A new PBG structure: Corrugated CPW, Microw Opt Tech Lett 39 (2003), D. Sievenpiper, L. Zhang, R.F.J. Broas, N.G. Alexopoulos, and E. Yablonovitch, High-impedance electromagnetic surfaces with a forbidden frequency band, IEEE Trans Microw Theor Tech 47 (1999), K. Kurokawa, Some basic characteristics of broadband negative resistance oscillator circuits, Bell Syst Tech J 48 (1969), Q. Xue, K.M. Shum, and C.H. Chan, Novel oscillator incorporating a compact microstrip resonant cell, IEEE Microw Wireless Compon Lett 11 (2001), Wiley Periodicals, Inc. NOVEL COUPLED FOLDED WAVEGUIDE RESONATOR FILTER Sultan Al-otaibi and Jia-Sheng Hong Department of Electrical, Electronic and Computer Engineering Heriot-Watt University Edinburgh EH14 4AS, The United Kingdom Received 22 February 2006 ABSTRACT: A novel four-pole bandpass filter design based on a coupled folded-waveguide (FWG) resonator structure is presented. A fullwave simulator has been employed for designing the filter and extracting the related coupling coefficient of each resonator pair. The proposed filter circuit design has been implemented. It has been found that the experimental results of constructed filter are in close agreement with the simulation and theoretical results. This filter also provides a low insertion loss with a much compact size compared with the conventional cavity filters. The theoretical, simulation and experimental results of the coupled FWG filter are presented Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: , 2006; Published online in Wiley InterScience ( DOI /mop Key words: coupled resonator filter; bandpass filter; folded-waveguide; FWG 1. INTRODUCTION High selectivity and low pass-band insertion loss of RF/microwave bandpass filters are required for many applications, including the rapidly expanding area of wireless communication systems. These requirements are imposed to conserve the valuable frequency spectrum and to enhance the performance of the systems. With the advent of micromachining techniques in fabricating microwave circuits, it is now possible to make miniature silicon micromachined high-q waveguide resonators [1 4] as building blocks for the development of high-performance microwave filters. The quality factor and the power handling that can be achieved with this type of resonator are much higher than that attainable with traditional microstrip resonators, either printed on a dielectric substrate or suspended in air with the support of a thin dielectric membrane. However, when compared with the membrane-supported microstrip resonator, the micromachined cavity resonator based on the conventional waveguide TE 101 mode is large in size, and particularly its footprint for many applications, such as for the development of multipole filters, it would be desirable to reduce the footprint of this type of resonator, since the height of micromachined cavity is usually quite small [5]. To this end, we present in this article a new four-pole bandpass filter design based on a coupled folded-waveguide (FWG) resonators. The proposed filter exhibits a symmetric frequency response and combines compact size and high quality factor. A demonstrator has been fabricated and tested. Theoretical, simulated, and measured results are presented. It is obvious that the proposed FWG resonator filter will be suitable not only for the micromach MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI /mop

2 Figure 1 (a) Configuration of four-pole FWG resonator filter and (b) coupling structure for the filter. [Color figure can be viewed in the online issue, which is available at ined devices but also for the waveguide devices fabricated using conventional techniques. 2. THEORY The proposed bandpass filter configuration and its coupling structure are shown in Figure 1. The filter is designed and implemented using four FWG resonators. Each of the FWG resonators [5] can maintain a fundamental resonant mode resembling TE 101 mode, with a smaller footprint only amounting to a quarter of that of the conventional TE 101 -mode cavity. Thus, the proposed four-pole filter has a size just about that of a conventional TE 101 -mode cavity operating at the same frequency. The filter is developed to realize the coupling structure of Figure 1(b). In this structure, there are three significant coupling coefficients between adjacent resonators, namely K 12, K 23, and K 34, which are realized through the opening gaps between adjacent FWG resonators, as can be seen from 3D viewing in Figure 1(a). The coupling coefficient k ij specifies the coupling between resonators i and j of the filter. When k ij is evaluated, only resonators i and j are considered in the structure. For the symmetry, the couplings between resonators 1 and 2 and between resonator 3 and 4 are identical. Thus, there are two basic coupling structures to be investigated. A filter of this type with a fractional bandwidth (FBW) of about 2.8% at a centre frequency of GHz has been successfully designed using a commercially available electromagnetic (EM) simulator [6]. The bandpass filter may be represented by an equivalent circuit as shown in Figure 2(a), where Q ei and Q eo are the external quality factors denoting the input and output couplings. The coupling coefficients and the external quality factors may be synthesized from a lowpass prototype filter, as shown in Figure 2(b), where the rectangular boxes represent frequency invariant immittance inverters defined through a transmission matrix [7]. In this work, a coupled FWG resonator bandpass filter is designed to have a FBW of 2.8% at a centre frequency f GHz. A four-pole (n 4) Tchebychev lowpass prototype with a passband ripple of db is chosen. We also have the values of g 0 1.0, g , g and J 12 J 34 1 and J 23 Figure 3 3-D layout of single-pole design. [Color figure can be viewed in the online issue, which is available at Figure 2 (a) An equivalent circuit of the four-pole resonator filter; (b) an associated low-pass prototype filter Figure 4 Typical frequency response simulated for extracting the external quality factor Q e. [Color figure can be viewed in the online issue, which is available at DOI /mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September

3 Figure 5 (a) 3-D layout of two-pole design. (b) Typical frequency response simulated for extracting the coupling coefficient. [Color figure can be viewed in the online issue, which is available at Figure 6 (a) The coupling coefficient at various cutting from both corners for fixed gap G (2.6 mm). (b) The coupling coefficient K 23 at various gap (G) for fixed corner cutting C (3.4 mm). [Color figure can be viewed in the online issue, which is available at The external quality factors and coupling coefficients of the bandpass filter can be calculated by Q ei Q eo g 0g 1 FBW, (1) K 12 K 34 FBW g 1 g 2, (2) This involved experimenting with the varied port position (L1) to achieve the desired external quality factor. The external quality factor was extracted from the simulated frequency response, as shown in Figure 4, based on the following formulation: f c Q e, (4) f 3dB K 23 FBW J 23 g 2. (3) Thus, the coupling coefficients for the adjacent resonators in the theory are K 12 K and K The external quality factors Q ei Q eo Q e EM SIMULATION, IMPLEMENTATION, AND RESULTS Using the design parameters obtained earlier, the implementation of the filter is carried out in several steps as described later. To realize the calculated external quality factor Q e 33.26, a single resonator with a tapped input arrangement (see Fig. 3) was simulated using a commercially available EM simulator [6]. Figure 7 Fabricated four-pole FWG resonator filter. Before assembly (a c) and after assembly (d). [Color figure can be viewed in the online issue, which is available at MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI /mop

4 Figure 8 Measured, EM simulated, and theoretical responses of the filter. [Color figure can be viewed in the online issue, which is available at where f c and f 3 db are the resonant frequency and the 3-dB bandwidth of the single resonator. The next step of the filter design was to characterize the desired couplings between adjacent FWG resonators for each pair of resonators (K 12 K and K ). This was done employing a two-pole filter model in Figure 5(a) with two input/output probes. Then the combination of coupling gap (G) between the resonators and corner cuttings (C) is varied to find the desired coupling coefficient from the simulated frequency response, as shown in Figure 5(b). The corner cuttings were introduced to compensate for the centre frequency shifting because of the coupling gap G. The coupling K ij of any pair of adjacent resonators was obtained from Ref. [7] as follows K ij f p2 2 f p1 2 f p2 2 f p1 2, (5) where f p1 and f p2 are the lower and higher split resonant frequencies of a pair of coupled resonators. Figure 6(a) depicts the extracted coupling coefficient K and central frequency f 0 against different cutting C from both corners of the inserted plate for a fixed coupling gap G 2.6 mm. One can see that the coupling coefficient K and central frequency f 0 almost increase linearly with the increase of cutting length C. A similar observation can be obtained for any other given G. Figure 6(b) depicts the extracted coupling coefficient K and central frequency f 0 against different coupling gap G between adjacent resonators for a fixed corner cutting C of 3.4 mm. It was noticed that the coupling coefficient (K) is directly proportional to the coupling gap length (G), whereas the central frequency f 0 is inversely proportional to G. For demonstration, the designed FWG resonator filter was fabricated from an industrial brass material, where the conductivity of brass is taken as S/m. Figure 7 shows the fabricated four-pole FWG resonator filter. It is composed of two identical halves, one of which is shown in Figure 7(a). The two halves with a recess of 4 mm are separated by a 1-mm-thick brass plate shown in Figure 7(b). Two SMA connectors as I/O ports are tapped to the plate as shown in Figure 7(c). The completely assembled filter, as illustrated in Figure 7(d), has a size of 61 mm 61 mm, including 6 mm-thick walls along all sides. The S-parameters of the fabricated FWG filter were measured using a calibrated HP network analyzer. Figure 8 plots the measured and EM simulated results along with the theoretical ones for comparison, where a good agreement between the measurement and simulation can be observed. The filter shows a desired symmetric frequency response with a low insertion loss in the passband. The measured insertion loss at the midband is about 1 db, including the losses from the two SMA connectors. The normalized frequencies are used in the plots for the theoretical centre frequency GHz, measured centre frequency of 4.39 GHz, and the simulated centre frequency of 4.49 GHz. The experiment was also carried out to measure the wide-band frequency response of the demonstrator, and the measured results are plotted in Figure 9. The following Table 1 compares frequency responses of the theoretical, simulated, and fabricated four-pole FWG resonator filter. The slight discrepancies are due to the tolerances in both fabrication and simulation. Figure 9 The wideband response Table 1 Comparison of Theoretical, Simulated, and Measured Results Theory Simulation Measurement f 0 (GHz) FBW DOI /mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September

5 4. CONCLUSIONS A new four-pole coupled FWG resonator filter has been designed, fabricated, and tested. Its design and implementation have been based on the full-wave EM simulation, and validated by the experiment. The measured and simulated results were in very good agreement. Owing to the high Q of the FWG resonators, the new filter has shown a low insertion loss in the passband with a very compact size. In this work, the proposed design procedure has been applied to a direct-coupled FWG filter, but it can also be extended to FWG filters with cross couplings. This new type of low loss and compact size filter is expected to be attractive for implementations with advanced device technologies, such as micromachining and LTCC. REFERENCES 1. J.P. Becker and L.P.B. Katehi, Toward a novel planar circuit compatible silicon micromachined waveguide, Proc IEEE Electrical Performance of Electronic Packaging, October 1999, pp M. Stickel, G.V. EIeftheriades, and P. Kremer, High-Q bulk micromachined sillicon cavity resonator at Ka-band, Electron Lett 37 (2001), J. Papapolymerou, J.-C. Cheng, J. East, and L.P.B. Katehi, A micromachined high-q X-band resonator, IEEE Microw Guid Wave Lett 7 (1997), C.A. Tavernier, R.M. Henderson, and J. Papapolymerou, A reducedsize silicon micromachined high-q resonator at 5.7 GHz, IEEE Trans Micorw Theor Tech 50 (2002), J.S. Hong, Compact folded-waveguide resonator, IEEE MTT-S Int Microw Symp Dig, Fort Worth, TX (2004). 6. Sonnet Software Inc., EM User s Manual, ver , New York, J.-S. Hong and M.J. Lancaster, Microstrip filters for RF/microwave applications, John Wiley, MA, Wiley Periodicals, Inc. REDUCED-SIZE RECONFIGURABLE TRI-BAND PRINTED ANTENNA WITH CPW TAPERED-FEED AND SHORTING POST J. A. Evans and M. J. Ammann Centre for Telecommunications Value-Chain Driven Research School of Electronic and Communications Engineering Dublin Institute of Technology, Kevin St. Dublin 8, Ireland 1. INTRODUCTION Convergence between mobile and portable wireless devices (e.g. mobile cellular and wireless LAN) creates a need for low-cost, multi-band antennas that can be easily integrated into portable packages. Printed planar monopole antennas are suitable for such applications because of their small size and flat structure. They have previously been shown to exhibit features of small antennas resonating in the range [1, 2]. A coplanar waveguide (CPW) is a convenient way of feeding a printed planar monopole antenna, allowing the ground plane elements to reside on the same side of the substrate as the monopole element. Dual-band CPW-fed planar monopole antennas have previously been proposed with 10-dB impedance bandwidths in the 5 GHz and 1.8 or 2.4 GHz bands [3 5]. The antenna investigated here is a variation of the printed planar monopole antenna, with a mismatched coplanar feed arrangement. In this article, the application of a shorting post and a notched area on the monopole element is investigated with respect to impedance bandwidth, radiation pattern, and reconfigurability. This antenna compares well in terms of size for the lower-edge frequency achieved. The longest overall dimension of the complete structure is (without shorting post), which is considered a small antenna. 2. ANTENNA STRUCTURE The CPW antenna (see Fig. 1) is constructed using low-cost printed circuit fabrication techniques and materials. The antenna substrate is a 1.52-mm-thick FR4, with a copper metalization thickness of 35 m (1 oz/sq. ft). The overall substrate size is 85 mm by 60 mm. The ground plane length (l g ) is 35 mm. The feed gap (g f ) between the ground-plane elements and the bottom edge of the monopole element was optimized at 3 mm for this antenna. The monopole element itself is optimized at mm 2 (w m l m ) for these applications. The monopole element is not centered on the feed structure; it is offset by 2.5 mm, which was found to increase the depth of the resonant modes without changing the other characteristics of the overall impedance bandwidth response. 2.1 CPW Feed Structure The CPW provides a convenient way of implementing an antenna feed on a printed structure with predetermined impedance. The application of a CPW feed of higher than 50 impedance has previously been shown to increase the impedance bandwidth of a Received 22 February 2006 ABSTRACT: A multiband printed monopole antenna is presented, operating primarily in the 900 MHz, 2.4 GHz bands, and 5 GHz bands. A coplanar waveguide feed arrangement is deployed, simplifying the antenna structure to a single side of a printed substrate material. Despite the small size of the antenna, a lower-edge frequency of 650 MHz is achieved. An impedance bandwidth of 63% is achieved in the 2.4-GHz band. The low profile antenna presented is potentially suitable for applications in modern mobile and portable radio systems that require operation over widely separated bands, combining multi-band operation with small size and low profile. With the application of a shorting post, the antenna has the potential for reconfigurable applications Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: , 2006; Published online in Wiley InterScience ( DOI /mop Key words: planar monopole; printed antenna; multiband antenna Figure 1 CPW monopole antenna geometry and coordinate system, showing the shorting post and notched area 1850 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI /mop